In the field of printing machines, a flexographic printing machine has been put to practical use. This type of printing machine is composed of a magnet roll whose surface is laminated with a magnet chip. To perform printing, a flexible printing plate containing a ferromagnetic material (e.g. iron, ferrite, cobalt, nickel) is attached (sucked) on the magnetic roll. An advantage of the flexographic printing machine resides in its capacity to change the print image in a simple manner, merely by replacing flexible printing plates.
With regard to printed matters, a face-cut label product as exemplified in FIG. 16 is widely available among the public. In this face-cut label product, a laminated sheet 110 is composed of a backing sheet 101 made of paper, transparent plastic sheet, etc., and a printing sheet 102 laminated thereon via an adhesive. Images are printed on the top surface of the laminated sheet 110. After the printing, the laminated sheet 110 is cut along profile lines 103 surrounding the printed images, in such a manner that the cutting reaches no further than the printing sheet 102 on the top. In use, a label portion defined by the profile line 103 on the printing sheet 102 is peeled off from the backing sheet 101, and the label can be affixed onto a notebook, day planner, photo album, slip, file index, etc.
Such face-cut label product is made by a combination of printing and cutting technologies. In one of the applicable methods, a rotary die cutter 160 is employed to perform the cutting operation in the printing machine. As illustrated in FIG. 18, a flexible die (rotary die) 161 is prepared by arranging push-cutting blades 162 in a predetermined pattern on one surface of a flexible base (ferromagnetic material) 164. The flexible die 161 is attached (sucked) on a die cylinder 166.
For the die cutter, a flat die cutter 170 shown in FIG. 19 can be used as well. The flat die cutter 170 is constituted with a top platen 172 for up-down movement and a bottom platen 174 fixed opposite to the top platen 172. The top platen 172 securely mounts a flexible die (flat die) 171. The flexible die 171 is composed of a flexible base 176 fixed on the top platen 172 and push-cutting blades 178 projecting in a predetermined pattern from one surface of the flexible base 176. On the other hand, the top surface of the bottom platen 174 holds a workpiece 179 in opposition to the flexible die 171. With the up-down movement of the top platen 172, the flat die cutter 170 cuts the workpiece 179 into a desired shape.
Flexible dies of these types include a punching die equipped with a continuous push-cutting blade, and a so-called perforating blade in which cutting portions and non-cutting portions are formed alternately along the cutting line. These flexible dies can be made by machining, etching, etc. A flexible die made by etching is generally called etched blade.
Now, the description is directed to an example of the method for manufacturing a flexible die (etched blade).
To begin with, a photoresist is uniformly laminated onto the surface of a steel or other metal plate. When this photoresist layer is exposed and developed, the metal plate surface retains a photoresist pattern exclusively for the push-cutting blade. Using the remaining resist pattern as a mask, the metal plate is etched away to a predetermined depth to its back surface. This etching step provides a flexible base and a trapezoid-section projection (rib) which protrudes from the flexible base. The resist pattern is removed at this stage.
Turning to FIG. 17, the trapezoid-section projection 221 has its tip sharpened by a conical tool 4. Thus obtained is a flexible die (punching die) in which the flexible base 201 is formed with a triangular-section push-cutting blade 202.
As mentioned above, the flexible die shown in FIG. 17 has the push-cutting blade 202 with a triangular cross section. However, this configuration is detrimental to precision machining. Namely, when a thick material is punched, the dimensions of the blank differ significantly between the top (front) and the bottom (back) around the machined area. In addition, the triangular configuration may deteriorate the blade durability, because such push-cutting blade is subjected to a heavy pressure during the punching operation.
The present invention is made in view of these circumstances, and intends to provide a flexible die which enables precision machining of even a thick material and which imparts excellent durability to the push-cutting blade. The present invention also intends to provide a method for manufacturing this flexible die.